Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$218.25	10.184%	$240.4766	$240.48	$240.50	$240.50
Purchase #2	$143.88	9.340%	$157.3184	$157.32	$157.30	$157.30
Purchase #3	$106.76	6.378%	$113.5692	$113.57	$113.55	$113.60
Purchase #4	$46.93	8.592%	$50.9622	$50.96	$50.95	$51.00
Purchase #5	$116.72	12.484%	$131.2913	$131.29	$131.30	$131.30
Purchase #6	$79.45	13.589%	$90.2465	$90.25	$90.25	$90.20
Purchase #7	$169.45	3.435%	$175.2706	$175.27	$175.25	$175.30
7 purchase totals =	$881.44		$959.1348	$959.14	$959.10	$959.20